U.S. patent application number 15/112926 was filed with the patent office on 2016-12-29 for apparatus and method for determining the liquid level of salvaged blood in a blood collection reservoir of an autologous blood transfusion system.
The applicant listed for this patent is FRESENIUS KABI DEUTSCHLAND GMBH. Invention is credited to Manfred Eirich, Melanie Fahrendorff, Artur Meisberger.
Application Number | 20160375185 15/112926 |
Document ID | / |
Family ID | 50151202 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160375185 |
Kind Code |
A1 |
Meisberger; Artur ; et
al. |
December 29, 2016 |
APPARATUS AND METHOD FOR DETERMINING THE LIQUID LEVEL OF SALVAGED
BLOOD IN A BLOOD COLLECTION RESERVOIR OF AN AUTOLOGOUS BLOOD
TRANSFUSION SYSTEM
Abstract
Disclosed is an apparatus and method for determining the liquid
level of salvaged blood in a blood collection reservoir (11) of an
autologous blood transfusion system (20), comprising sensing means
(10, 12) for periodically sensing the liquid level of the salvaged
blood in said blood collection reservoir (11) and outputting
corresponding signals, and determining means (2) for determining
the liquid level of the salvaged blood in said blood collection
reservoir (11) based on said output signal of said sensing means.
The sensing means comprises a plurality of light emitters (12)
disposed on a first side of said blood collection reservoir (11) at
different height levels (L1-L9) for emitting light and a plurality
of light receivers (10) disposed at said different height levels
(L1-L9) on a second side of said blood collection reservoir (11)
opposite to said first side for sensing light emitted by said light
emitters (12) and transmitted through said blood collection
reservoir (11). Parameters of the optical set-up used for detection
and signal analysis may be adjusted individually and dynamically so
that disturbing effects caused e.g. by absorptive films on the
inner surface of the blood collection reservoir (11) may be
identified and prevented to thereby enhance the reliability of
signal detection and analysis.
Inventors: |
Meisberger; Artur; (St.
Wendel, DE) ; Fahrendorff; Melanie; (Niederkassel,
DE) ; Eirich; Manfred; (Freiensteinau, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FRESENIUS KABI DEUTSCHLAND GMBH |
Bad Homburg |
|
DE |
|
|
Family ID: |
50151202 |
Appl. No.: |
15/112926 |
Filed: |
December 17, 2014 |
PCT Filed: |
December 17, 2014 |
PCT NO: |
PCT/EP2014/078124 |
371 Date: |
July 20, 2016 |
Current U.S.
Class: |
250/341.7 |
Current CPC
Class: |
A61M 1/3627 20130101;
A61M 2205/18 20130101; A61M 2205/3313 20130101; A61M 2205/3306
20130101; A61M 2205/3389 20130101; A61M 1/0259 20130101; G01F
23/2924 20130101; A61M 2205/52 20130101 |
International
Class: |
A61M 1/02 20060101
A61M001/02; G01F 23/292 20060101 G01F023/292 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2014 |
EP |
14156384.1 |
Claims
1. An autologous blood transfusion system for the recovery and
washing of salvaged blood collected from a surgical site of a
patient, comprising: a blood collection reservoir for storing the
collected blood, an optical detection setup for periodically
detecting a liquid level of the salvaged blood in said blood
collection reservoir and for outputting a corresponding output
signal, and a processor for determining the liquid level of the
salvaged blood in said blood collection reservoir based on said
output signal of said optical detection setup, said optical
detection setup comprising: a plurality of light emitters disposed
on a first side of said blood collection reservoir at different
height levels for emitting light and a plurality of light receivers
disposed on a second side of said blood collection reservoir
opposite to said first side for sensing light emitted by said light
emitters and transmitted through said blood collection reservoir
and for outputting said output signal.
2. The autologous blood transfusion system as claimed in claim 1,
wherein said light emitters are pulsed light emitters for emitting
light pulses, preferably infrared light pulses, wherein: said
optical detection setup is configured for switching said light
emitters on and off individually in correspondence to a control
signal, and said processor is configured for analyzing output
signals outputted by light receivers that correspond to said light
emitters individually and in correspondence with said control
signal.
3. The autologous blood transfusion system as claimed in claim 1,
wherein said processor is configured for: reading-out output
signals of said light receivers sequentially along a vertical
direction of said blood collection reservoir, comparing said output
signals with a predetermined threshold value, and determining the
liquid level of the salvaged blood in said blood collection
reservoir based on said comparing said signals with said
predetermined threshold value.
4. The autologous blood transfusion system as claimed in claim 1,
wherein said processor is configured for individually adjusting
detection parameters associated with said plurality of light
emitters and said plurality of light receivers, said detection
parameters including at least one of an output power of said light
emitters, a gain of an amplifier used for amplifying output signals
outputted by said plurality of light receivers and a threshold
value used by said processor.
5. The autologous blood transfusion system as claimed in claim 4,
wherein said processor is further configured for: identifying a
conspicuous signal out of said output signals of said light
receivers based on a comparison of output signals of at least two
light receivers out of said plurality of light receivers, varying a
detection parameter of a light emitter and/or of a light receiver
and/or of an amplifier associated with said conspicuous signal, and
repeating said step of determining the liquid level of the salvaged
blood in said blood collection reservoir using said varied
detection parameter.
6. The autologous blood transfusion system as claimed in claim 5,
wherein said processor is further configured for: determining the
liquid level of the salvaged blood in said blood collection
reservoir using said varied detection parameter if a signal of a
light receiver or amplifier associated with said varied detection
parameter is not identified as a conspicuous signal in said
identifying step when repeating said step of determining the liquid
level of the salvaged blood in said blood collection reservoir
using said varied detection parameter.
7. The autologous blood transfusion system as claimed in claim 1,
wherein the processor is further configured for starting or
controlling a washing process based on said liquid level determined
by said processor, particularly upon reaching preset liquid levels
in the blood collection reservoir, or for generating a warning
message and outputting said warning message via an interface, if
the liquid level determined by said processor indicates a complete
or nearly complete depletion of the blood collection reservoir.
8. A method for determining a liquid level of salvaged blood in a
blood collection reservoir of an autologous blood transfusion
system, comprising a plurality of light emitters disposed on a
first side of said blood collection reservoir at different height
levels for emitting light and a plurality of light receivers
disposed on a second side of said blood collection reservoir
opposite to said first side for detecting light emitted by said
light emitters and transmitted through said blood collection
reservoir, said method comprising: periodically activating said
plurality of light emitters for emitting light; detecting light
transmitted through said blood collection reservoir using said
plurality of light receivers; and determining the liquid level of
salvaged blood in the blood collection reservoir based on output
signals outputted by said plurality of light receivers.
9. The method as claimed in claim 8, wherein said light emitters
are switched on and off individually in correspondence to a control
signal to thereby emit light pulses, in particular infrared light
pulses, and wherein output signals outputted by light receivers
that correspond to said light emitters are analyzed individually
and in correspondence with said control signal.
10. The method as claimed in claim 8, further comprising:
reading-out output signals output by said light receivers
sequentially along a vertical direction of said blood collection
reservoir; comparing said output signals with a predetermined
threshold value; and determining the liquid level of the salvaged
blood in said blood collection reservoir based on said step of
comparing said output signals with said predetermined threshold
value.
11. The method as claimed in claim 8, further comprising:
individually adjusting detection parameters associated with said
plurality of light emitters and said plurality of light receivers,
said detection parameters including at least one of an output power
of said light emitters, a gain of an amplifier used for amplifying
output signals outputted by said plurality of light receivers and a
threshold value used for determining the liquid level.
12. The method as claimed in claim 11, further comprising:
identifying a conspicuous signal out of said output signals of said
light receivers based on a comparison of output signals of at least
two adjacent light receivers out of said plurality of light
receivers; varying a detection parameter of a light emitter and/or
of a light receiver and/or of an amplifier associated with said
conspicuous signal; and repeating said step of determining the
liquid level of the salvaged blood in said blood collection
reservoir using said varied detection parameter.
13. The method as claimed in claim 12, further comprising:
determining the liquid level of the salvaged blood in said blood
collection reservoir using said varied detection parameter if a
signal of a light receiver or amplifier associated with said varied
detection parameter is not identified as a conspicuous signal in
said identifying step when repeating said step of determining the
liquid level of the salvaged blood in said blood collection
reservoir using said varied detection parameter.
14. The method as claimed in claim 8, wherein a washing process is
started or controlled based on said liquid level determined by said
processor, particularly upon reaching preset liquid levels in the
blood collection reservoir, or wherein a warning message is
generated and output via an interface, if the liquid level
determined by said processor indicates a complete or nearly
complete depletion of the blood collection reservoir.
15. A computer program product for use in an autologous blood
transfusion system for determining a liquid level of salvaged blood
in a blood collection reservoir of said autologous blood
transfusion system, said computer program product comprising
computer program code means for performing a method according to
claim 8, if executed in a processor or control unit of said
autologous blood transfusion system.
Description
FIELD OF INVENTION
[0001] The present invention relates in general to an autologous
blood transfusion system and method for the recovery and washing of
salvaged blood collected from a surgical site of a patient and
relates particularly to an enhanced method for determining the
liquid level of the salvaged blood in a blood collection reservoir
of an autologous blood transfusion system.
BACKGROUND OF INVENTION
[0002] Autologous blood transfusion systems (autotransfusion
devices) are widely used for the recovery and washing of salvaged
blood collected from a patient particularly at a surgical site,
where a large volume blood loss can be expected--e.g. aneurysm,
total joint replacement, and spinal surgeries. In such systems the
salvaged blood is temporarily stored in a blood collection
reservoir for re-use. A reliable determination of the liquid level
or volume of the salvaged blood in the blood collection reservoir
is crucial for surgeries. Inter alia it is important to avoid a
complete depletion of the blood collection reservoir. Furthermore,
a reliable process control in such systems requires exact
information on the liquid level or volume of the salvaged blood in
the blood collection reservoir.
[0003] For this purpose often the weight of the blood collection
reservoir is monitored by means of a controller and upon reaching
predetermined or pre-calibrated threshold values the controller
outputs signals for further process control.
[0004] An example for such an approach is disclosed in U.S. Pat.
No. 5,458,566, wherein the weight of the blood collection reservoir
is monitored using a strain gage device to compute the volume of
fluid present in the reservoir. When it is determined that a
sufficient volume of fluid is present in the reservoir, the system
initiates a new FILL cycle. The washing method of this
autotransfusion device is not continuous but discontinuous. Thus,
the response time of the volume measurement can be slower. The
blood collection reservoir is supported vertically by a radially
inner support member and is subject to vertical forces during
system operation. The device further comprises a radially outer
support member secured to a mounting surface. The strain gage is
coupled between the inner support member and outer support member
for sensing vertical strain forces therebetween and converting
vertical forces originating with the tubes into horizontal forces.
Around the blood collection reservoir many different conduits are
arranged, to which personnel at the surgical site must have free
and quick access e.g. for security reasons. This somehow
contradicts the requirements of a smooth and steady environment
required by the strain gage device itself. Thus, it is difficult to
ensure a robust and reliable determination of the liquid level or
volume of salvaged blood in the blood collection reservoir.
[0005] EP 2531823 A1 of the applicant discloses a method and
apparatus for the capacitive level measurement of a liquid medium
in a bubble trap of a dialysis machine.
[0006] U.S. Pat. No. 4,275,726 of the applicant discloses an
apparatus and method for balancing the fluids withdrawn from a
patient and the fluids simultaneously returned into the patient for
use in exchange blood transfusion, infusion therapy in conjunction
with forced diuresis or haemofiltration. In this approach the
liquid level of a liquid reservoir used for temporarily storing a
liquid is sensed by means of a row of radiation emitters and a row
of radiation receivers disposed on a side of the liquid reservoir
opposite to the radiation emitters, which generate an output signal
representative of the transmission at the various different height
levels of the collection reservoir. Use of this method for
autotransfusion devices is not disclosed. Furthermore, problems
caused by obstruction of the light beams transmitted through the
reservoir caused e.g. by a blood or lipid film on the inner surface
of the reservoir are not handled.
[0007] Thus, there exists a need for more robust and reliable
concepts for determining the liquid level of salvaged blood in a
blood collection reservoir of autologous blood transfusion systems
(autotransfusion devices).
SUMMARY OF INVENTION
[0008] It is an object of the present invention to provide an
enhanced autologous blood transfusion system and method using a
robust and reliable apparatus and method for determining the liquid
level of salvaged blood in a blood collection reservoir of such an
autologous blood transfusion system. It is a further object of the
present invention to provide a computer program product for use in
such an autologous blood transfusion system for determining the
liquid level of salvaged blood in a blood collection reservoir.
[0009] This problem is solved by an autologous blood transfusion
system according to claim 1, by a method for determining the liquid
level of salvaged blood in a blood collection reservoir of such an
autologous blood transfusion system as claimed by claim 8 and by a
computer program product as claimed by claim 15. Further
advantageous embodiments are the subject-matter of the dependent
claims.
[0010] According to the present invention there is provided an
autologous blood transfusion system for the recovery and washing of
salvaged blood collected from a surgical site of a patient,
comprising a blood collection reservoir for storing the collected
blood, an optical detection setup for periodically detecting the
liquid level of the salvaged blood in said blood collection
reservoir optically, particularly by means of measuring the
transmission of light beams, particularly of pulsed light beams,
passing through the blood collection reservoir and outputting a
signal in correspondence to signals detected by said optical
detection setup, and a processor for determining the liquid level
of the salvaged blood in said blood collection reservoir based on
said output signal of said sensing means, said optical detection
setup comprising a plurality of light emitters disposed on a first
side of said blood collection reservoir at different height levels
for emitting light and a plurality of light receivers disposed on a
second side of said blood collection reservoir opposite to said
first side for sensing light emitted by said light emitters and
transmitted through said blood collection reservoir and for
outputting said output signal.
[0011] Use of an optical detection set-up enables a more robust and
reliable determination of the liquid level of salvaged blood in a
blood collection reservoir. In particular, no mechanical elements,
coupling members or sensors are required. Furthermore, the optical
set-up enables a fully opto-electronic signal detection and a fully
electronic signal analysis, which offers additional advantages,
such as simple but reliable variation of the measurement conditions
and parameters used for signal analysis.
[0012] Preferably, the light emitters and light sensors are
disposed at regular spacings along the vertical direction of the
blood collection reservoir and are distributed over the entire
height of the blood collection reservoir. According to further
embodiments, however, the light emitters and light sensors may also
be disposed at a given higher density in regions that are
considered to be of particular importance for assessment of the
process conditions in the blood collection reservoir or for a
precise signal analysis. The light receivers (sensors) are disposed
spaced apart from each other and may be disposed at the same
different height levels as the light emitters.
[0013] According to a further embodiment the light emitters are
pulsed light emitters for emitting light pulses, preferably
infrared light pulses, particularly short light pulses of a
duration of e.g. 50 .mu.sec, so that the amount of energy, which is
deposited in the salvaged blood, can be reduced significantly.
Furthermore, the measurement can be performed periodically at
frequencies that are significantly different to those of noise
sources, such as mains current, fluorescent tubes or other kinds of
light sources typically used at surgery sites. Furthermore, the
processor is configured for switching the light emitters on and off
individually in correspondence to a control signal, which switches
on and off the light emitters, and said processor is further
configured for analyzing signals output by light receivers that
correspond to the light emitters individually and in correspondence
with such a control signal. Thus, the conditions can be determined
more reliable as a function of the vertical height level along the
blood collection reservoir.
[0014] According to a further embodiment the processor is
configured for a) reading output signals of said light receivers
sequentially along a vertical direction of said blood collection
reservoir, b) comparing said output signals with a predetermined
threshold value, and c) determining the liquid level of the
salvaged blood in said blood collection reservoir based on said
comparing said output signals with said predetermined threshold
value. The threshold value enables a reliable discrimination of
transmission changes in the sequence of output signals read-out
from the plurality of light receivers and can be varied and
re-adjusted easily, so that the method can be used for various
different process conditions.
[0015] According to a further embodiment the processor is
configured for individually adjusting detection parameters
associated with the plurality of light emitters and the plurality
of light receivers. As will be shown in the following, this enables
to suppress the disturbing effects particularly of absorptive films
of contaminants, such as fat or clotted blood, on the inner surface
of the blood collection reservoir, which otherwise could result in
wrong or even misleading information. According to the present
invention these detection parameters include at least one of an
output power of the light emitters, a gain of an amplifier used for
amplifying output signals output by the plurality of light
receivers and a threshold value used by the determining means for
analyzing the output signals output by the plurality of light
receivers.
[0016] According to a further embodiment the processor is further
configured for a) identifying a conspicuous signal out of said
output signals of said light receivers based on a comparison of the
output signals of at least two light receivers out of said
plurality of light receivers (which may be directly adjacent light
receivers), b) varying a detection parameter of a light emitter
and/or of a light receiver and/or of an amplifier associated with
said conspicuous signal, and c) repeating said step of determining
the liquid level of the salvaged blood in said blood collection
reservoir using said varied detection parameter. In the sense of
the present application a conspicuous signal is a signal that
indicates abnormal transmission changes between output signals of
at least two (preferably at least three) directly adjacent light
receivers or sequences of at least two (preferably at least three)
transmission values that might be caused by blood or lipid films on
the inner surface of the storage vessel or similar effects locally
perturbing the optical transmission through the storage vessel.
[0017] According to a further embodiment the processor is further
configured for determining the liquid level of the salvaged blood
in said blood collection reservoir using said varied detection
parameter if a signal of a light receiver or amplifier associated
with said varied detection parameter is not identified as a
conspicuous signal in said identifying step when repeating said
step of sensing the liquid level of the salvaged blood in said
blood collection reservoir using said varied detection
parameter.
[0018] According to a further embodiment the processor further
comprises a look-up-table for determining conditions of the
collected blood collected in the blood collection reservoir based
on a comparison of the respective output signal with contents of
the look-up-table. The contents of the look-up-table may
particularly reflect the typical transmission (or absorption)
characteristics of typical process conditions or contaminants that
might occur in the blood collection reservoir, and might be
knowledge-based or result from an initial calibration or training
method performed prior to the measurement method. As an example: if
the output signals outputted by a series of light receivers are in
accordance with a typical transmission expected to occur below the
filling level, i.e. within the salvaged blood stored in the storage
vessel of the system, and if the signal outputted by an
intermediate light receiver of said series of light receivers
indicates an exceptionally higher or lower transmission that would
otherwise indicate air or a rather thick blood at the height level
of the corresponding light receiver in the storage vessel, the
output signal of this intermediate light received is considered as
a conspicuous signal, indicating an abnormal or unusual
transmission change at the height level of the intermediate light
receiver that requires a specially dedicated measuring procedure at
this height level for further discriminating the reason for this
abnormal or unusual transmission change at the height level of the
intermediate light receiver.
[0019] According to a further embodiment the processor is further
configured for starting or controlling the washing process based on
said filling level, particularly upon reaching preset filling
levels in the storage vessel, or for generating a warning message
and outputting said warning message via an interface, if the filing
level measured indicates a complete or nearly complete depletion of
the storage vessel.
[0020] A further aspect of the present invention relates to a
corresponding method for determining the liquid level of salvaged
blood in a blood collection reservoir of such an autologous blood
transfusion system as described in the following.
[0021] A further aspect of the present invention relates to a
corresponding computer program product for determining the liquid
level of salvaged blood in a blood collection reservoir of such an
autologous blood transfusion system as described in the
following.
BRIEF OVERVIEW ON DRAWINGS
[0022] Hereinafter the invention will be described with reference
to exemplary embodiments and referring to the enclosed drawings,
wherein:
[0023] FIG. 1 schematically shows an apparatus for determining the
liquid level of salvaged blood in a blood collection reservoir of
an autologous blood transfusion system according to the present
invention;
[0024] FIG. 2 is a partial cross-sectional view of an inner wall
portion of the blood collection reservoir of FIG. 1 with a
contamination caused by a blood or lipid film on the inner surface
of the blood collection reservoir;
[0025] FIG. 3 is a schematic flow diagram of a method for
determining the liquid level of salvaged blood in a blood
collection reservoir of an autologous blood transfusion system
according to the present invention; and
[0026] FIG. 4 schematically shows a washing chamber of an
autologous blood transfusion system comprising a blood collection
reservoir, wherein the liquid level of the salvaged blood in the
blood collection reservoir is determined in accordance with the
present invention.
[0027] Throughout the drawings, identical reference numerals
designate identical or substantially equivalent elements or groups
of elements
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Before describing a method for determining the liquid level
of salvaged blood in a blood collection reservoir of an autologous
blood transfusion system according to the present invention, in the
following the general environment of utilizing such a method in an
autologous blood transfusion system or autotransfusion device will
be described briefly with reference to FIG. 4, which shows a
washing chamber of such an autologous blood transfusion system
using a continuous flow technique for washing blood.
[0029] More specifically salvaged blood that has been e.g.
collected from a surgical site of a patient, enters a continuous
washing process in which red blood cells are resuspended with a
saline solution and blood plasma and other contaminants are
removed. The salvaged blood is pumped by pump 28 from the reservoir
for collected blood 11 via conduit 28 to enter the washing process
together with a washing solution pumped by pump 28 from reservoir
22 via conduit 28. In this process blood is concentrated to a
haematocrit (HCT) of e.g. approx. 80% and most of the blood plasma,
cellular debris, white blood cells, platelets, anticoagulant and
other unwanted constituents are separated out. Furthermore, a
removal of non-emulsified fat as complete as possible is performed.
Red cells from a red cell concentrate stored in reservoir 24 are
packed to a HCT concentration of e.g. 60-65%. The recovered blood
is then infused into the patient's body at a different site (not
shown).
[0030] The blood collection reservoir 11 in this process is a
transparent storage vessel and may be a standard reservoir
utilizing a special double lumen suction tubing, wherein fluid is
aspirated from the operative field and is mixed with an
anticoagulant solution. Collected fluid is filtered in a sterile
cardiotomy reservoir. The reservoir contains a filter and has a
capacity of between two and three liters of fluid. The blood
collection reservoir 11 may have a conical funnel-shaped
bottom.
[0031] FIG. 1 shows a setup for determining the liquid level or
volume of salvaged blood in the blood collection reservoir 11 used
in an autologous blood transfusion system as described above with
reference to FIG. 4. The storage vessel 11 is filled with salvaged
blood together with a washing solution. The longer the washing
process is employed in the above washing process, the more the
volume in the reservoir 11 separates into the following regions:
salvaged blood having a high HCT 18, particularly with
sedimentation at the bottom of storage vessel 11, salvaged blood
having a low HCT 17, with HCT values even close to a clear plasma
solution, and a layer of foam 16 on top of the surface of the
salvaged blood. The layer of foam 16 may have a thickness of up to
1-2 centimeters. During the washing process the filling level of
the salvaged blood in the storage vessel 11 repeatedly moves
upwards and downwards. When moving upwards and downwards, portions
with films of e.g. clotted blood 14 or lipid 15 may remain locally
on the inner surface of the storage vessel 11.
[0032] For measuring the filling level (volume) of the salvaged
blood in the storage vessel 11, the transmission of light through
the storage vessel 11 is measured by means of an optical setup.
More specifically, a plurality of light emitters 12, such as
light-emitting diodes (LEDs), are disposed on a first side of
storage vessel 11 at different height levels indicated by reference
numerals L1-L9, which emit light beams preferably in the infrared
wavelength range to reduce deposition of radiation energy in the
salvaged blood. The transmitted light intensity is measured by a
plurality of light receivers 10, such as photodiodes, disposed on a
side of the storage vessel 11 opposite to the light emitters 12.
Hereinafter, in order to identify the light receivers 10 and light
emitters 12, respectively, at the respective height levels L1, L2,
. . . Ln, these light receivers and light emitters are named 10.1,
10.2, . . . 10.n and 12.1, 12.2, . . . 12.n, respectively. The
light emitters 12 and light receivers 10 may be disposed in a
protective housing that may be sleeved onto the storage vessel 11,
which is usually a disposable, and is configured for re-use. The
light emitters 12 and light receivers 10 may be disposed at the
same height levels L1-L9.
[0033] An array of electronic switches 13 is associated with the
light emitters 12 so that the light emitters can be switched on and
off individually by means of control signals of controller 2
transmitted via transmission line 5. A further array of electronic
switches 9 is associated with the light receivers 10 so that the
transmission signals output by the light receivers 10 can be
read-out individually via transmission line 4. The read-out
transmission signals are amplified by an amplifier 3 using a gain
factor that can be adjusted by the controller 2 via control line 7.
More specifically, the transmission signals output by different
light receivers 10.1, . . . 10.n can be amplified individually by
means of gain factors individually adjusted for each of the light
receivers 10.1, . . . 10.n.
[0034] For determining the filling level or volume of salvaged
blood in the storage vessel 11, the output signals of the light
receivers 10.1, . . . 10.n are analyzed for determining a
transition from a relatively low transmission (indicating a certain
absorption of light by salvaged blood) to a relatively high
transmission (indicating no absorption of light by salvaged blood).
More specifically, the output signals of the light receivers 10.1,
. . . 10.n are read-out sequentially along a vertical direction of
the storage vessel, e.g. in the order starting with the lowest
sensor L.1 to the uppermost sensor L.n or in the opposite order,
and a transition from relatively low transmission to relatively
high transmission is determined, i.e. where a transition from dark
regions to less absorptive regions occurs, which corresponds to the
actual filling level in the storage vessel 11 or e.g. to the
transition from salvaged blood to saline solution. For this
purpose, algorithms may be used which use a threshold value for
discriminating between signals indicating a relatively low
transmission and signals a relatively high transmission. According
to a first embodiment the light beams emitted by the light emitters
12 are collimated light beams or nearly collimated light beams
having a small beam divergence. Thus, the light receivers 10
disposed on a side of the storage vessel 11 opposite to said light
emitters 12 may be disposed at the same height levels L1-L9 as the
light emitters 12 and may detect only of one light beam transmitted
through the storage vessel 11 and emitted by the directly opposite
light emitter. According to a preferred second embodiment, however,
the light emitters 12 emit highly divergent light beams, e.g. of a
divergence angle of 120.degree., in which case the light receivers
10 on the opposite side of the storage vessel 11 may detect the
light beams emitted by several light emitters 12. More
specifically, the light receivers 12 disposed in the central part
of the storage vessel, such as light receivers 12 disposed at
height levels L5 or L6, may detect the light beams emitted by two
or even more of the directly opposite light emitters, such as light
emitters 12 disposed at height levels L4-L6 (for the light receiver
disposed at height level L5) and light emitters 12 disposed at
height levels L5-L7 (for the light receiver disposed at height
level L6). As will be shown in the following, according to the
present invention the relatively high divergence angle of the light
beams emitted by the light emitters may further assist to more
easily and reliably discriminate conspicuous signals caused
particularly by blood or lipid films on the inner surface of the
storage vessel 11, which result in locally abnormal transmission
changes.
[0035] Based on the above information the washing process may be
started or performed e.g. upon reaching preset filling levels in
the storage vessel 11 or at filing levels without saline solution
supernatant. The bottom light receiver (at height level L1) or a
bottom light receiver (at height level L0) are used for indicating
a complete depletion of the storage vessel 11, in which case a
warning message is generated by controller 2 and outputted via
interface 1 to external devices, such as displays, alarm devices or
the like. For this purpose, it may be of advantage, if the bottom
of the storage vessel 11 is slanted, conically tapered and the
bottom light receiver 10 at height level L0 measures the
transmission in the region of the slanted, conically tapered bottom
of the storage vessel 11.
[0036] More specifically, the washing process may be started only
if a predetermined minimum filling level is initially provided in
the storage vessel 11, which may correspond to a liquid volume of
e.g. 0.75 l or 1 l. By means of the measured filling level the
washing process is controlled such that a minimum filling level of
e.g. 50 ml in the storage vessel 11 is ensured during the whole
process or surgery and that a complete depletion of the storage
vessel 11 is always prevented, e.g. in order to avoid the presence
of air or foam in centrifuge used in the washing process or at the
locations of sensors, which might otherwise give rise to wrong or
misleading signals. Thus, the washing process may be interrupted
temporarily, if a nearly complete depletion of the storage vessel
11 is determined based on the sensed filling level, e.g. if only
the bottom light receiver 10 at height level L0 indicates a filling
level but none of the other light receivers 10 at the other height
levels L1-L9. As a result of such a temporary interruption of the
washing process the filling level in the storage vessel 11 will
rise again due to the collecting of additional salvaged blood from
the patient at the surgical site, until a predetermined upper
filling level is reached again finally, e.g. corresponding to a
volume of 0.75 l or 1 l, which triggers again the washing process.
The above loop may be repeated until a user, particularly an
anesthetist, inputs a signal to controller 2 via interface 1 that
the washing process shall be terminated, e.g. if it has been
decided that the surgery will be terminated shortly.
[0037] FIG. 2 is a partial cross-sectional view of a wall portion
of the storage vessel 11 of FIG. 1 with a contamination caused by
blood or lipid films 14, 15 on the inner surface of the storage
vessel 11. These blood or lipid films 14, 15 result in a locally
reduced transmission of the sensing light emitted by the light
emitters 12, which is independent of the transmission (absorption)
of the content of the storage vessel at given height level. These
blood or lipid films 14, 15 are independent of the actual filling
level in the storage vessel 11 and may remain on the inner surface
even above the actual filling level, if the filling level of
salvaged blood shrinks to a lower height level, as shown in FIG. 1.
A repeated movement of the surface of the salvaged blood upwards
and downwards during the washing process, even results in the
agglomeration of such blood or lipid films 14, 15 on the inner
surface of the storage vessel 11. As shown in FIG. 2, the presence
of blood film 14 at the height level L4 of light receiver 10.4
results in a reduced transmission of the sensing light beam B.4 as
compared to the transmission of the sensing light beams B.3 and B.5
at the height levels L3 and L5, respectively. This results in
measurement of an incorrect transmission ratio at height level L4,
which can cause a wrong or even misleading discrimination
(determination) of the actual filling level in the storage vessel
11 or of the transition from salvaged blood to saline solution
inside the storage vessel 11, which is to be prevented.
[0038] According to the present invention the sequential
reading-out of the transmission signals from the light receivers 10
along the vertical direction of the storage vessel 11 may be used
to identify conspicuous signals at height levels, which are not in
accordance with standard transmission profiles in the storage
vessel to be expected under normal operating conditions and which
otherwise might result in a wrong or even misleading discrimination
of the actual filling level in the storage vessel 11 or of the
transition from salvaged blood to saline solution inside the
storage vessel 11. It should be noted that such standard
transmission profiles in the storage vessel to be expected under
normal operating conditions may be stored in a look-up table
[0039] If one assumes e.g. for the state shown in FIG. 2 that light
receivers 10.3-10.5 are above the actual filling level in the
storage vessel 11, then the signals of light receivers 10.3 and
10.5 will indicate a relatively high transmission that might even
correspond to a transmission of 100% (if one takes into account
reflection losses at the various interfaces), whereas the signal of
light receiver 10.4 will indicate a relatively low transmission.
Under normal conditions in the storage vessel 11 such a sequence of
transmission values at height levels L3-L5 cannot be the result of
normal transmission changes near the actual liquid surface in the
storage vessel 11. Rather, the controller 2 will assume that the
signal corresponding to light beam BA is a conspicuous signal and
that no transition region exists at these height levels, as
outlined in the following. In the sense of the present application
conspicuous signals are signals that indicate abnormal transmission
changes between signals of at least two (preferably at least three)
directly adjacent light receivers 12 or sequences of at least two
(preferably at least three) transmission values that might be
caused by blood or lipid films on the inner surface of the storage
vessel 11 or similar effects locally perturbing the optical
transmission through the storage vessel 11.
[0040] As another example, if one assumes e.g. for the state shown
in FIG. 2 that light receivers 10.3-10.5 are below the actual
filling level in the storage vessel 11, then the signals of light
receivers 10.3 and 10.5 will indicate a transmission typical for
salvaged blood, which is already relatively low, whereas the signal
of light receiver 10.4 will indicate an even lower transmission
that might even be zero and is caused by the additional presence of
blood film 14 at the height level L4 corresponding to light
receiver 10.4. Under normal conditions in the storage vessel 11
such a sequence of transmission values at height levels L3-L5
cannot be the result of transmission changes near the actual liquid
surface in the storage vessel 11. Rather, the controller 2 will
assume for such a measured signal that the signal corresponding to
light beam B.4 is a conspicuous signal and that no transition
region exists at these height levels, as outlined in the following,
and will consider the transmission measured at height level L4 as a
conspicuous transmission.
[0041] In order to discriminate a conspicuous signal at height
level L4 caused by a zero or abnormally low (conspicuous)
transmission, the following approach may be pursued.
[0042] For this purpose, in the following it is assumed that
usually the transmission values at the different height levels
L3-L5 in FIG. 2 are measured by means of individual light beams
B.3-B.5 that are selectively turned on for measuring the
transmission at a given height level. More specifically, light beam
B.3 at height level L3 is used for measuring the transmission by
means of associated light receiver 10.3, light beam B.4 at height
level L4 is used for measuring the transmission by means of
associated light receiver 10.4 and light beam B.5 at height level
L5 is used for measuring the transmission by means of associated
light receiver 10.5. If a zero transmission or conspicuously low
transmission is measured at height level L4, the measurement of the
transmission is repeated with all light beams B.3-B.5 turned on. As
the light beams B.3-B.5 have a relatively high divergence angle (of
e.g. 120.degree.), a certain percentage of the power of adjacent
light beams B.4 and B.6 will propagate to light receiver 10.4 at
height level L4. Thus, the total light power available at height
level L4 for measuring the transmission at this height level is
temporarily increased, which also holds for the total light powers
available at the neighboring height levels. At the increased light
power the transmission measured at height level L4 might not be
zero but non-vanishing. A comparison with the transmission values
measured at the neighboring height levels L3 and L5 and analyzing
the transmission values finally results in information, whether the
conspicuous signal at height level L4 previously measured is the
result of a film on the inner surface of the storage vessel 11 or
not. For future measurements of the transmission at height level L4
the higher power for beam L4 may be used.
[0043] As will become apparent to a person skilled in the art, a
similar discrimination may also be obtained, if the other
parameters relevant for the detection of the light beams
(hereinafter detection parameters) are varied, particularly the
output power of the light emitters and/or the gain of amplifiers
used for amplifying signals output by the respective light
receivers and/or a threshold value used by the processor or
controller 2 for analyzing the output signals of the light
receivers.
[0044] As will become apparent to a person skilled in the art, a
similar discrimination may also be obtained, if the light beams
emitted by the light emitters are not highly divergent light beams
but instead collimated or nearly collimated light beams.
[0045] As will become apparent to a person skilled in the art, a
similar approach, which varies the detection parameters for
detecting the transmission at the different height levels
individually or collectively, may also be used to discriminate
other conditions of the content of the storage vessel, such as the
degree of dilution of the salvaged blood contained in the storage
vessel 11.
[0046] FIG. 3 is a schematic flow diagram of a method for
determining the liquid level of salvaged blood in a storage vessel
of an autologous blood transfusion system (autotransfusion device)
according to the present invention, which preferably uses a
continuous washing process. For sensing the transmission signals of
the light receivers at height levels L1-Ln, detection parameters
are used, which in a first cycle are predetermined, e.g. based on a
previous calibration step for calibrating all light receivers at
height levels L1-Ln for equal sensitivity. In the sense of the
present application, these "detection parameters" may be any of an
output power of the light emitters 12, a gain of an amplifier 3
used for amplifying signals output by the light receivers 10 and a
threshold value used for analyzing the (amplified) output signals
of the light receivers 10 in the controller 2, or any other
suitable parameter relevant for signal detection and analysis.
According to the present invention, these detection parameters are
not fixed values but may be adjusted individually for the light
receivers L1-Ln and may be adjusted even dynamically while
performing the washing process, as will be described in the
following.
[0047] Referring to FIGS. 1 and 3, in step S1 the transmission at
the height levels L1-Ln of light receivers 10 is detected and
further analyzed by controller 2 utilizing predetermined detection
parameters. For this purpose the signals of the light receivers 10
at height levels L1-L9 are preferably read-out in a given order,
e.g. sequentially in vertical direction of the storage vessel 11
from bottom to top or top to bottom. Based on this set of
transmission values the controller performs a signal analysis in
step S2 using suitable algorithms, for identifying the presence and
height level (location) of light sensors indicating conspicuous
changes of transmission that are candidates for a wrong or even
misleading discrimination of the actual filling level in the
storage vessel 11 or of the transition from salvaged blood to
saline solution inside the storage vessel 11. For this purpose the
analysis may proceed e.g. as described with reference to FIG. 2
above.
[0048] If no such conspicuous changes of transmission or
conspicuous signals are determined in step S2, then the method
proceeds with step S3, in which the controller 2 considers the
measured transmissions at the height levels L1-Ln of light
receivers 10 as correct and not-misleading and uses the measured
transmissions for determining the actual filling level in the
storage vessel 11 or the transition from salvaged blood to saline
solution inside the storage vessel 11 for further signal
processing.
[0049] The loop of steps S1-S3 is performed periodically, to
thereby obtain information on the actual filling level in the
storage vessel 11 or on the transition from salvaged blood to
saline solution inside the storage vessel 11 periodically. For this
purpose, the light emitters 12 preferably emit short light pulses,
at a repetition rate that is substantially different to the
frequency of a mains current, to the operation frequency of
fluorescent tubes or other kinds of light sources typically used at
surgery sites, or to higher harmonics thereof. Thus, disturbing
background noise is suppressed and a higher signal-to-noise ratio
can be accomplished. As an example, 100 .mu.s infrared light pulses
at a repetition rate of 25 Hz may be used in a method according to
the present invention.
[0050] On the other hand, if in step S2 the controller 2 determines
at least one conspicuous change of transmission based on the
transmission values measured using the predetermined detection
parameters, then the method proceeds with step S4 for varying the
detection parameters and with steps S5 and S6 for repeating the
above identification of conspicuous changes of transmission.
[0051] In the following, the state shown in FIG. 2 is considered,
in which the presence of blood film 14 at the height level L4 of
light receiver 10.4 results in a reduced transmission at height
level L4 compared to the transmission detected at the height levels
L3 and L5, respectively, and it is assumed that the controller 2
identifies height level L4 as a location of a conspicuous change of
transmission (conspicuous signal). In such a state, in step S4 the
detection parameters at height level L4 are varied and the
transmission is measured and analyzed in step S5 using such varied
detection parameters.
[0052] As a first example, the output power of light emitter 12 at
height level L4 is selectively increased and/or the gain of
amplifier 3 used for amplifying the signal output by light receiver
10 at height level L4 is increased and/or a threshold value used
for analyzing the (amplified) output signal of the light receiver
10 at height level L4 in the controller 2 is selectively adjusted
in step S4 and the transmission is measured and analyzed in step S5
using such varied detection parameters. If the controller analyzes
a transmission for the varied detection parameters that is a
typical transmission of salvaged blood, saline solution, foam or
air and such a typical transmission behavior has already been
observed in step S1 for the adjacent height levels L3 and L5,
respectively, then in step S6 no such conspicuous change of
transmission is identified at height level L4. Rather, the method
proceeds with step S7 to adjust the detection parameters at height
level L4 to the new detection parameters used in step S5 and
proceeds again with step S1, in which case in step S2 no such
conspicuous change of transmission will be identified anymore at
height level L4, but rather the method will proceed with step
S3.
[0053] As a second example, the output powers of light emitters 12
at height levels L3-L5 are selectively increased and/or the gain
factor of amplifier 3 used for amplifying the signals output by
light receiver 10 at height levels L3-L5 are selectively increased
and/or the threshold values used for analyzing the (amplified)
output signals of the light receiver 10 at height levels L3-L5 in
the controller 2 are selectively adjusted in step S4 and the
transmission is measured and analyzed in step S5 using such varied
detection parameters. Using the varied detection parameters a far
better signal-to-noise ratio is available for a more reliable
determination whether the change in transmission at height level L4
results from an actual transition region in the storage vessel 11
or simply from an undesired film 14 on the inner surface of storage
vessel 11. For this purpose, the transmission values at height
levels L3-L5 are compared with each other in step S5 and analyzed
further.
[0054] Thus, in the second example, if the controller analyzes a
transmission for the varied detection parameters that is a typical
transmission of salvaged blood, saline solution, foam or air and
such a typical transmission behavior has already been observed in
step S1 for the adjacent height levels L3 and L5, respectively,
then in step S6 no such conspicuous change of transmission is
identified at height level L4. Rather, the method proceeds with
step S7 to adjust the detection parameters at height level L4 to
the above varied detection parameters and to readjust the detection
parameters at the adjacent height levels L3 and L5, respectively,
to those detection parameters used previously in step S1. Then the
method proceeds again with step S1, in which case in step S2 no
such conspicuous change of transmission will be identified anymore
at height level L4, but rather the method will proceed with step
S3.
[0055] If finally, despite the variation of the detection
parameters in step S4, still a conspicuous change of transmission
is determined in step S6, an error handling routine S8 may be
triggered, which will not be described here in detail, but which
may comprise outputting an error signal for indicating an
unreliable or error state of the measuring system, triggering a
supplemental cleaning procedure for cleaning the inner surface of
the storage vessel 11, e.g. by rinsing the inner surfaces with a
washing solution, or for stopping operation of the washing
procedure and issuing a warning/stop signal to the personnel at the
surgical site.
[0056] The above loop of steps S1-S7 may be repeated several times,
until the controller determines that at least one of the detection
parameters runs beyond a predetermined parameter range. Then, the
above error handling routine S8 may also be triggered. The process
may then return to step S1.
[0057] As will become apparent to a person skilled in the art, in
case of detection of a conspicuous change of transmission in step
S2, the detection parameters may be varied in step S4 and/or the
further transmission signal analysis may be performed based on
knowledge data or calibration data on the typical transmission
characteristics in the presence of the standard types of
contaminants and conditions of the salvaged blood during the
washing process. Such knowledge data may be stored e.g. in a
look-up-table (not shown) to which the controller 2 has access or
in a memory coupled to or integrated in controller 2.
[0058] By means of varying the detection parameters selectively at
different height levels, the filling level (volume) of salvaged
blood or the transition from salvaged blood to saline solution
inside the storage vessel 11 may be determined reliably even under
adverse conditions that otherwise would result in incorrect or even
misleading measurements and signal analysis.
[0059] The approach of varying the detection parameters selectively
at different height levels may also be used for calibrating the
optical detection setup shown in FIG. 1. If one assumes that the
light beams emitted by light emitters 12 are highly divergent, it
is apparent that more light will strike on the central light
receives 10 and that less light will strike on those light
receivers 10 that are disposed at the upper and lower end of the
storage vessel 11, such as the light receivers at height levels Ln
and L1, respectively. This may be compensated by increasing the
power emitted by the correspondingly opposite light emitters 12,
i.e. light emitters 12 disposed at height levels Ln and L1,
respectively, or the gain of amplifiers used for amplifying the
signals output by the light receivers disposed at height levels Ln
and L1, respectively.
[0060] As will become apparent to a person skilled in the art, the
possibility of selectively varying the detection parameters at
height levels according to the present invention even makes it
possible to derive additional information about the content of the
storage vessel 11 at the height levels, such as an analysis of the
HCT at the different height levels, the saline concentration at the
different height levels or similar parameters of the salvaged
blood.
LIST OF REFERENCE NUMERALS
[0061] 1 Interface/Power supply [0062] 2 Controller/Determining
means [0063] 3 amplifier [0064] 4 transmission line [0065] 5
transmission line [0066] 6 transmission line [0067] 7 control line
for adjusting gain of amplifier [0068] 8 transmission line [0069] 9
array of switches [0070] 10 array of light receivers [0071]
10.3-10.5 light receivers at height levels L3-L5 [0072] 11 blood
collection reservoir [0073] 12 array of light emitters [0074] 13
array of switches [0075] 14 blood film (in blood collection
reservoir) [0076] 15 lipid film (in blood collection reservoir)
[0077] 16 foam (in blood collection reservoir) [0078] 17 region
with low haematocrit (in blood collection reservoir) [0079] 18
region with high haematocrit (in blood collection reservoir) [0080]
20 autologous blood transfusion system [0081] 21 rotating washing
chamber [0082] 22 reservoir for washing solution [0083] 23 waste
bag [0084] 24 reservoir for red cell concentrate [0085] 25 pump
[0086] 26 pump [0087] 27 pump [0088] 28 tubing [0089] L1-Ln height
levels [0090] L0 height level of bottom light receiver [0091]
B.3-B.5 sensing light beams at height levels L3-L5
* * * * *